You can get plywood in many different qualities and versions. The price differs a lot depending on what you choose. The different qualities are normally designate in accordance with the surfaces and the core.
The most superior plywood for boat building is of course marine plywood. For a large variety of applications it is excellent but for some applications it might be overkill to use marine plywood.
For most of the boats here on Boatplans.dk it is fully acceptable to use exterior grade plywood. It is always recommended to prime the plywood with epoxy resin in order to make the plywood moister resistant.
I have for many of my boats used cheap Brazilian plywood in grade B/C and it has worked fine without any problems. The different grades can be read in the table below, and the B/C means that one side B-grade and the other is C-grade.
Grade N veneers
Grade N veneer shall be smoothly cut 100% heartwood or 100% sapwood, free from knots, knotholes, pitch pockets, open splits, other open defects, and stain. The veneer shall consist of not more than two pieces in 1220 mm (48-inch) widths and not more three pieces in wider panels, and shall be well matched for color and grain.
Grade A veneers
Grade A veneer shall be firm; smoothly cut; and free of knots, pitch pockets, open splits, and other open defects and well jointed when of more than one piece.
Grade B veneers
Grade B veneer shall be solid and free from open defects and broken grain, except repaired smaller splits, openings, knots and cracks or checks. Slightly rough grain shall be permitted. Minor sanding and patching defects shall not exceed 5% of panel area.
Grade C veneers
Sanding defects shall not impair the strength or serviceability of the panel.
Grade C Plugged veneers
Knotholes, worm and borer holes, and other open defects; sound and tight knots; split; broken grains; pitch pockets; plugs; patches and shims shall be permitted. Where grades having C Plugged face veneer are fully sanded, sanding defects shall be the same as admitted under B grade.
Grade D veneers
Any number of plugs, patches, shims, worm or borer holes, sanding defects, and other characteristics shall be permitted, provided they do not seriously impair the strength or serviceability of the panel.
The requirements above are not a fully description of the grades but an abstract of the requirements.
One thing you must always remember is to buy plywood that are glued with water and boiling proof glue. That is normally stated with a WBP mark.
Most of the designs from Boatplans.dk do not require glass fabric on the entire hull. Basically it is a choice omitted because the fabric often makes the finish work more difficult. For most designs the strength of the plywood is more than enough for the boat.
It is however possible to cover the hull with a glass fabric in order to obtain better durability and easier maintenance over the years. If you choose so my advice will be to choose a crowfoot woven light fabric. Furthermore the crowfoot weave has the advantage that it is totally invisible when wetted out with resin.
For the designs that require glass fabric a biaxial ±45° glass fabric is chosen. The fabric consists of two layers of glass laid perpendicular to each other and in an angel of ±45° to to the warp direction. The two layers are stitched together.
The fabric gives an outstanding and strong laminate. Furthermore it is easy to work with and very flexible. It requires some finish work after it is wetted out and the laminate is dry, but when wetted out and rolled carefully the finish work can be kept at a minimum.
The glass tape specified can be of any regular available type. One thing that is important is that the tape you choose has a minimum weight as specified under the different designs. If your normal supplier does not have the weight specified choose the nearest weight above the one specified.
Epoxy resin for your new boat can be bought from many suppliers and manufactures. Choose the supplier where you get the best service and guidance, also if something turns out not exactly as you suspected.
You can get epoxy resin with different hardeners. Some are meant for slow cure and some for fast. If you can't find a hardener with a curing time that fits your need it is often possible to mix the hardener. This means that if you would like to have a gel time between the slow and fast hardener you simply mix the two and achieve a gel time in between.
Some manufactures produce a special tropic hardener. It is very suitable for laminating in warm areas. You will then have time to apply and work with the epoxy even if the temperature reaches 43°C (109F).
The amount of resin is, for the metric units, given in kg. Some suppliers give the amount in litres. As an approximation you can make 1 litre equal 1.1 kg. This means the other way around that 1 kg is equal 0.9 litres.
The filler is applied to the epoxy resin in order to make it thicker. The thickened epoxy resin is used for making fillets between the panels and the frames.
For most of our designs you can use ordinary wood flour. Basically the wood flour is some fine and very clean sawdust, and in principles you can make it yourself. But it is recommended to buy it from your supplier since you get a very clean product without any impurity.
For some of our designs the filler specified is Aerosil or Carbosil. It is important to use Aerosil or Cabosil because the fillet needs some structural properties that the filler will apply to the epoxy resin. Adding Aerosil or Cabosil to the epoxy makes it harder to grind, therefore the best thing to do is to smooth the fillets carefully before they harden.